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Replumbing a heating system, Sizing a pump

Mudaero
Mudaero Member Posts: 46
Hey guys. Been reading a lot here and learning more. I am hoping someone can answer some general and specific questions about my hydronic system. Sorry if this is long-winded.

I am finishing my basement and removing the old steel supply and return lines that feed CI radiators. In addition, I will also be adding fin-tube radiators in the basement. I will be running pex-al-pex to all elements. The largest radiator produces about 15,000 btu/h, the smallest, 3,000. There are 7 radiators in the system. There will be 4 baseboard radiators, the total element length about 45'. The total estimated BTU for the house is about 80,000 (including basement). I plan on having 3 zones (basement, main, upstairs). Boiler is an older NG, Weil-McClain HE Series 3 (100,000 BTU AGA, 82,000 DOE). It needs a new circulator pump.

My biggest concern is finding the right pex tube size. Along with that, I will need a new circulator pump and I will be adding the zones, so I need to make sure I get the right pump and do the zones correctly. If I run a circuit to each element, the longest run would be about no more than 70' (it's a small house). I'm not sure if I am doing my head loss correctly for the circulator because that longest run is upstairs and more than half of the run is 1" steel pipe (not sure how to do mixed piping in the calculation).

Can anyone help me determine what size pex would be sufficient and help me with pump sizing based on that recommendation? With the two different elements (CI and fin-tube) should there be two circulator pumps? Or is one sufficient? I will most likely do the zones with zone valves and manifolds (any suggestion on those are appreciated), or with the pumps if 2 are required. Is my boiler sufficient? I'd imagine it is, but I would just like some opinions. It works fine, but should I think about replacing it?

Basically, throw any opinions and expertise at me. I'd truly appreciate it. I will be talking to a professional about this, but I'll be doing as much of the work as I can and I'd like to be well informed before talking to him.

Thanks for reading.

Comments

  • Mudaero
    Mudaero Member Posts: 46
    Thanks for the response, Hatterasguy. You are correct in assuming I summed all of the radiators. While this is probably incorrect as to the amount my house truly needs, I am located in one of the coldest parts of the country (Upper Peninsula Michigan, on Lake Superior), and it is an older house (but updated) but you're right, it probably is larger than what is really needed.

    I didn't think replacing the boiler was necessary, I just wanted to get some other opinions. It works perfectly fine and does not run 100% on the coldest day. The only issue is the circulator pump hums (which can be heard throughout the house), so I just figured I would replace it while I am rebuilding the new system.

    Would you feel that one circulator pump in this system is sufficient? My thought is that it would be. Is the zone valves to manifolds a better idea than a trunk and branch?

    I appreciate your input.
  • Mudaero
    Mudaero Member Posts: 46
    Excellent information. Thank you. Yes, the lines from the boiler will be 1" copper to the manifold, and the zone valves will be on these 1" lines. I appreciate you taking the time to help me on this. I just need to do my calculations now to get the correct pump size and should be good to go. I will definitely look at the Grundfos Alpha as a replacement. Thanks again for your help.
  • Mudaero
    Mudaero Member Posts: 46
    Very good. One other question. You stated earlier that I could get enough BTU on the 1/2" pex line at 1.5 GPM (which makes perfect sense). When calculating head loss, would I use the entire system needs (so the GPM would be 8) or would I just do this by the circuit that needs the most GPM (the 1.5)?
  • Mudaero
    Mudaero Member Posts: 46
    I think I stated that poorly. I meant, when sizing the pump and doing the head loss calculations, would I use the 8 GPM or the 1.5 GPM on the pump curve table.